A cast product having an amorphous or glassy molecular structure, in the form of a relatively thin elongated strip or ribbon, has proven to be effective for winding into highly efficient cores for electrical transformers of other uses. Some of the most recent developments in the casting of amorphous or glassy metal ribbons are reviewed in U.S. Pat. No. 4,332,848.
As is known the casting of ribbons having an amorphous or glassy structure requires the application of a particularly high chill rate to the ribbon on the order of 10.sup.5 -10.sup.6 .degree. C./sec. Further, this chill rate must be provided throughout the entire thickness of the ribbon if a continuous glassy structure is to be obtained. Consequently, the thickness of amorphous cast ribbons is limited by these extreme heat transfer requirements. If proper heat transfer is not maintained some crystallization occurs, thus destroying the amorphous structure.
While these thin cast glassy ribbons may be wound into highly efficient transformer cores, increased stacking or packing densities are possible with thicker ribbons in order to further increase the efficiency of the transformer, and generally to lower the cost. These advantages are deemed to make it worthwhile to seek a way to sucessfully make thicker amorphous metal ribbon.
U.S. Pat. No. 4,185,185 to Adlam and U.S. Pat. No. 4,187,408 to Heile disclose a continuous seam welding process for binding two strips of sheet material such as aluminum, that converge at a V between two nip rolls. The nip rolls apply pressure at the point of convergence and a laser beam is focused into the converging V.
The Adlam and Heile patents do not teach or suggest a method for the fabrication of thick glassy metallic ribbons from two or more glassy metallic ribbons. In other words, the prior art fails to recognize or consider how to deal with the peculiar properties of amorphous or glassy material when forming a thick ribbon. There is no teaching or suggestion of special treatment and parameters of operation during welding if the glassy structure is to be retained through the entire body of the ribbon.
In order to weld glassy metallic ribbons together so that the resulting product is a single glassy metallic body, the nature of the heat transfer characteristics of the system and the properties of the glassy material must be considered. If the integrity of the amorphous molecular structure of the material is to be maintained, the crystallization temperature of the material must not be exceeded. Also, because of the slow heat transfer rates that may be expected between the ribbon and the external environment, the ribbon has to be self-quenching or cooling. Additionally, with heat from the ribbon surface during welding rapidly dispersing into the ribbon body, the ribbon must be moving at a rapid rate so that the molten surfaces forming the weld zone can come into contact before they re-solidify. Therefore, the welding together of two strips of amorphous metal ribbon so that the product remains amorphous may only take place within certain parameters, relating to the welding energy, drawing rate and cooling rate.